Excellent! You have selected the correct
answer. Sir Mello Yello Bug correctly determined that this was
a big drop for BLUE. He heard the other bug's comments,
so he knew BLUE had 4 men left in his inner board. And Sir Mello
Yello Bug saw that only BLUE had another checker left in
the outfield (notice his view from the bugpile).
If you counted all of BLUE'S checkers, you saw that only 10 men
had been taken off. That means 5 more BLUE men were still on the
board somewhere. Counting is an important part of backgammon.

Always remember JENSEN'S LAW:

"There are three kinds of backgammon players in the world:
those who can count, and those who cannot."